U.S. patent application number 15/778951 was filed with the patent office on 2018-11-29 for high-pressure and high-temperature closed geothermal exchanger for a magmatic or metamorphic formation.
This patent application is currently assigned to BRGM. The applicant listed for this patent is BRGM. Invention is credited to Denis Nguyen.
Application Number | 20180340711 15/778951 |
Document ID | / |
Family ID | 55542800 |
Filed Date | 2018-11-29 |
United States Patent
Application |
20180340711 |
Kind Code |
A1 |
Nguyen; Denis |
November 29, 2018 |
High-Pressure And High-Temperature Closed Geothermal Exchanger For
A Magmatic Or Metamorphic Formation
Abstract
The invention relates to a geothermal exchanger comprising a
casing containing a heat-transfer fluid with which it is in direct
contact. The casing is flexible such as to be in direct contact
with a wall of the borehole containing the exchanger under the
effect of the pressure of the heat-transfer fluid.
Inventors: |
Nguyen; Denis; (Montpellier,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRGM |
Orleans Cedex 2 |
|
FR |
|
|
Assignee: |
BRGM
Orleans Cedex 2
FR
|
Family ID: |
55542800 |
Appl. No.: |
15/778951 |
Filed: |
November 22, 2016 |
PCT Filed: |
November 22, 2016 |
PCT NO: |
PCT/FR2016/053045 |
371 Date: |
May 24, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24T 10/17 20180501;
Y02E 10/125 20130101; F24T 10/15 20180501; Y02E 10/10 20130101;
F24T 10/13 20180501; F28F 21/062 20130101 |
International
Class: |
F24T 10/15 20060101
F24T010/15; F24T 10/17 20060101 F24T010/17; F28F 21/06 20060101
F28F021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2015 |
FR |
1561294 |
Claims
1. A closed geothermal exchanger for a magmatic or metamorphic
formation, comprising a shell containing a heat-transfer fluid with
which it is directly in contact, wherein the shell is flexible so
that it can be in direct contact, under the effect of the pressure
of the heat-transfer fluid with a wall of a borehole containing the
exchanger.
2. The geothermal exchanger as claimed in claim 1, the flexible
shell having a shore A hardness of between about 60 and about
90.
3. The geothermal exchanger as claimed in claim 1, the upper part
of the exchanger comprising a containment device designed to limit
the expansion of the flexible shell.
4. The geothermal exchanger as claimed in claim 3, the containment
device comprising a containment harness which, at least in part,
caps the upper part of the exchanger.
5. The geothermal exchanger as claimed in claim 4, the containment
harness comprising aramid straps, and preferably from Kevlar
straps.
6. The geothermal exchanger as claimed in claim 1, the flexible
shell comprising silicone elastomer.
7. The geothermal exchanger as claimed in claim 6, the silicone
elastomer having a thermal conductivity higher than 3.5
W/(m.K).
8. The geothermal exchanger as claimed in claim 1, further
comprising an inner tube into which the heat-transfer fluid is
injected, the inner tube comprising a bottom part with an opening
that allows the heat-transfer fluid to pass toward the outside of
the inner tube.
9. The geothermal exchanger as claimed in claim 8, the inner tube
comprising a silicone elastomer having a thermal conductivity of
about 0.2 W/(m.K).
10. The geothermal exchanger as claimed in claim 1, the temperature
of the heat-transfer fluid being greater than 100.degree. C.
Description
FIELD OF THE INVENTION
[0001] mon The present invention relates to the field of the
diffusive geostorage of heat, namely storage with no exchange of
matter with the subsoil, which involves closed geothermal
exchangers through which there circulates a heat-transfer fluid
that exchanges its heat with the sub-soil encasing the
exchanger.
BACKGROUND OF THE INVENTION
[0002] What is meant by a closed geothermal exchanger is an
exchanger that uses a heat-transfer fluid that circulates not in
the surroundings but in sealed underground pipes. The heat-transfer
fluid of these systems therefore does not form part of the
geological surroundings. As a matter of principle, the
heat-transfer fluid that circulates in a closed system is always
the same and represents a limited volume. In the case of a closed
geothermal exchanger, there is no exchange of matter between the
exchanger and the environmental surroundings.
[0003] The only geostorage operations performed at the present time
are the diffusive geostorage of heat using pressurized water as the
heat-transfer fluid (Borehole Thermal Energy Storages--BTES). These
geothermal exchangers are made up of coaxial U-shaped tubes, or
tubes having another geometry, typically made of high density
polyethylene (PEND) or any other rigid material.
[0004] The boreholes in the subsoil in which these tubes are placed
are plugged with a hydrated cement the purpose of which is to
provide thermal coupling between the wall of the rigid tube that
constitutes the exchanger and the wall of the borehole.
[0005] Existing closed geothermal exchangers are ill suited to
operating temperatures in excess of 100.degree. C. because of the
thermal coupling with the encasing rocky massif which is performed
by way of a hydrated cement which would experience impediment of
its geomechanical properties above and beyond 100.degree. C.
[0006] This is why, at the present time, the temperatures of the
heat-transfer fluid in operations involving the diffusive
geostorage of heat using pressurized water as the heat-transfer
fluid in the closed geothermal exchangers are generally comprised
between 50.degree. C. and 70.degree. C. The pressure in the
exchangers is of the order of ten bar or so.
[0007] However, there is a need for closed geothermal exchangers in
which the heat-transfer fluid can be at a temperature higher than
100.degree. C.
[0008] Thus, for example, for the in-massif storage of electricity
by thermal pair as described in document FR 3009613, the "hot" pole
of the thermal pair is a heat geostore using closed geothermal
exchangers. The heat-transfer fluid in the geothermal exchangers is
carbon dioxide (CO.sub.2) in a supercritical state, at a
temperature that can be as high as 140.degree. C., and at a
pressure that can be as high as 120 bar.
[0009] The heat-transfer fluid could also be superheated steam. The
temperature in the exchanger could then, for example, reach
240.degree. C.
SUMMARY OF THE INVENTION
[0010] The object of the invention is to provide a closed
geothermal exchanger the operation of the heat-transfer fluid of
which can be at a temperature higher than 100.degree. C.
[0011] To that end, the subject of the invention is a closed
geothermal exchanger for a magmatic or metamorphic formation,
comprising a shell containing a heat-transfer fluid with which it
is directly in contact. The exchanger is characterized in that the
shell is flexible so that it can be in direct contact, under the
effect of the pressure of the heat-transfer fluid, with a wall of a
borehole containing the exchanger.
[0012] What is meant by a "flexible shell" is a shell that has a
shore A hardness comprised between 60 and 90.
[0013] What is meant by a "magmatic formation" is a formation
resulting from the crystallization of a magma.
[0014] What is meant by a "metamorphic formation" is a formation
that has undergone a transformation in the solid state as a result
of an increase in temperature and/or pressure, notably with the
crystallization of new minerals.
[0015] The exchanger has the geomechanical strength properties
necessary for being placed in direct contact with the magmatic or
metamorphic formation.
[0016] When pressurized by the heat-transfer fluid, the wall of the
shell, or bladder, is pressed firmly into contact with the rocky
massif, thus providing thermal coupling between the exchanger and
the encasing rocky massif, without requiring thermal coupling
material between the geothermal exchanger and the rocky massif. The
device is thus simplified in comparison with devices that have
coupling material.
[0017] The borehole in which the geothermal exchanger is placed is
a vertical borehole.
[0018] The magmatic rock or the metamorphic rock in which the
borehole is made is a healthy rocky outcrop, at zero meters. It is
not an altered formation. There is no soil on the top. If there is
a layer of plant matter, this is stripped off before the borehole
is made.
[0019] The injection and return of the heat-transfer fluid are
performed at the same end of the geothermal exchanger, at its upper
end at the surface.
[0020] This end is said to be at the surface because it is oriented
toward the ground, as opposed to the other end which is oriented
toward the depth.
[0021] Advantageously, the upper part of the exchanger comprises a
containment device designed to limit the expansion of the flexible
shell.
[0022] The containment device is able to withstand the internal
pressure in the exchanger applied to the upper part of the
bladder.
[0023] In one embodiment, the containment device is made up of a
containment harness which, at least in part, caps the upper part of
the exchanger.
[0024] As a preference, the containment device extends over a
length from 1 m to 3 m from the upper end of the exchanger.
[0025] That part of the containment device that is situated below
ground level is held in place by being squashed between the
exchanger bladder pressurized by the heat-transfer fluid, and the
wall of the borehole.
[0026] Optionally, the containment harness is made from aramid
straps, such as Kevlar straps.
[0027] Advantageously, the geothermal exchanger extends over a
length from 10 to 30 m.
[0028] According to one embodiment, it may extend over a length
from 12 to 30 m. According to another embodiment, it may extend
over a length from 10 to 20 m.
[0029] Its diameter is from 20 to 50 cm, preferably from 20 to 30
cm.
[0030] The thickness of the wall of the bladder is from 10 mm to 50
mm, preferably from 10 to 30 mm.
[0031] Advantageously, the flexible shell is made of silicone
elastomer.
[0032] That material has all the thermomechanical strength
qualities required to operate at high temperatures (up to at least
250.degree. C.) and high pressures (up to at least 150 bar), and
has a high coefficient of elasticity allowing the wall of the
bladder of the geothermal exchanger to conform as closely as
possible to the wall of the encasing rocky massif once the bladder
has been pressurized by the heat-transfer fluid in the exchanger. A
geothermal exchanger such as this can therefore be used in the case
of projects for the diffusive geostorage of heat at temperatures
higher than 100.degree. C., whether using superheated steam or
CO.sub.2 in a supercritical state.
[0033] In this embodiment, a silicone elastomer having an increased
thermal conductivity, notably higher than 3.5 W/(m.K), is chosen so
that it is similar to the thermal conductivity of granite.
[0034] Optionally, the geothermal exchanger also comprises an inner
tube into which the heat-transfer fluid is injected. The inner tube
is provided in its bottom part with an opening that allows the
fluid to pass toward the outside of the inner tube.
[0035] Such a device allows the exchanger to be adapted to suit
boreholes which may reach depths of 30 m.
[0036] For preference, the inner tube has an inside diameter of 120
to 200 mm depending on the diameter of the geothermal exchanger.
Advantageously, the inside diameter of the inner tube is 120 mm for
an exchanger diameter of 20 cm, and 200 mm for an exchanger
diameter of 30 cm.
[0037] In general, the diameter of the inner tube is determined so
that the loss of pressure head in the flow between entering the
exchanger and exiting the exchanger (namely the sum of the losses
in pressure head in the inner tube and in the annular space) is
minimal.
[0038] Advantageously, the inner tube is made from a flexible
material such as silicone elastomer. For the manufacture of the
inner tube, a silicone elastomer with a low thermal conductivity,
notably of between 0.15 and 0.25 W/(m.K) is chosen, so as to limit
heat losses internal to the geothermal exchanger.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The invention will be better understood from studying the
attached figures, which are provided by way of entirely nonlimiting
example, in which:
[0040] FIG. 1 is a view in longitudinal section of a closed
geothermal exchanger according to one embodiment of the
invention.
[0041] FIG. 2 is a view in longitudinal section of a closed
geothermal exchanger according to a second embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0042] Reference is now made to FIG. 1 which shows a closed
geothermal exchanger 1 according to one embodiment of the
invention. The geothermal exchanger comprises a shell 2 containing
CO.sub.2 in a supercritical state 3 (supercritical CO.sub.2) used
as a heat-transfer fluid. The shell 2 and the heat-transfer fluid 3
are in direct contact.
[0043] The shell 2 is made of a silicone elastomer which is a
flexible material the shore A hardness of which is comprised
between 60 and 90. However, it could be made from any other
material that gives it the flexibility it needs to come into direct
contact, under the effect of the heat-transfer fluid, with the wall
of the borehole.
[0044] The silicone elastomer used to make the shell 2 has a
thermal conductivity higher than 3.5 W/(m.K). This value is similar
to the thermal conductivity of granite.
[0045] The heat-transfer fluid may be any heat-transfer fluid
chemically compatible with silicone elastomer, which may have a
temperature ranging as high as at least 250.degree. C. and a
pressure of up to at least 150 bar.
[0046] The geothermal exchanger 1 is installed in a vertical
borehole 4 made in a granite formation 5. Under the effect of the
pressure of the supercritical CO.sub.2 fluid 3, the shell 2 is
brought into direct contact with the wall of the borehole 4. The
injection 6 and return 7 of the heat-transfer fluid 3 are performed
at the surface end 8 of the upper part of the shell 2.
[0047] The upper part of the exchanger 1 is contained within a
containment harness 9 made of Kevlar straps. It may be made of
other aramid straps. The straps used have a width of 1 cm and their
cumulative width is 40 cm. The straps could have a different width.
The containment harness constitutes a containment device the shape
of which could be other than that of a harness.
[0048] The containment harness 9 extends over the upper part of the
shell, including its surface end 8. It extends over a length L1 of
1 m and is wedged between the bladder 2 and the granite formation
5.
[0049] The shell 2 extends over a length L2 of 20 m. This length
may be different. It may vary from 10 to 20 m. Its diameter d is 20
cm. It may be different and vary from 20 to 30 cm. The thickness of
its wall is 10 mm. It may be different and vary from 10 to 30
mm.
[0050] For an internal pressure of 120 bar in the shell 2, the load
on the upper part of the exchanger 20 cm in diameter in contact
with atmospheric pressure is 38 000 daN. The Kevlar straps used
have a tensile strength of 1000 daN per cm of width. A cumulative
width of around 40 cm of straps distributed over the 62 cm of
circumference of the bladder 2 makes it possible to compensate for
the load on the upper part of the exchanger. As it is pressurized,
when the bladder 2 is not yet pressed firmly against the wall of
the hole, the resistance of the bladder 2 to stretching is enough
to keep the bladder 2 and the heat-transfer fluid 3 inside the
borehole 4. When the bladder 2 is pressed against the wall of the
borehole 4 by 120 bar of internal pressure, the bladder 2 is held
in place by the resistance of the walls of the borehole and by the
resistance of the containment harness 9. As the length of strap
wedged between the bladder 2 and the granite formation 5 is 1 m,
the area of straps subjected to the pressure of 120 bar is 100
cm.sup.2, which corresponds to a crushing force on the strap of 12
000 daN, which means that a tensile force of 1000 daN on the strap
can be withstood.
[0051] FIG. 2 shows a closed geothermal exchanger 1' according to
another embodiment of the invention. The exchanger 1' comprises a
shell 2' containing supercritical CO.sub.2 fluid 3'. The shell 2'
and the heat-transfer fluid 3' are in direct contact.
[0052] The shell 2' is made of silicone elastomer with a shore A
hardness comprised between 60 and 90. It could, however, be made
from any other material that gives it the flexibility that allows
it to come into direct contact, under the effect of the
heat-transfer fluid, with the wall of the borehole.
[0053] The silicone elastomer used to make the shell 2' has
increased thermal conductivity, higher than 3.5 W/(m.K).
[0054] The heat-transfer fluid may be any heat-transfer fluid
chemically compatible with silicone elastomer, which may have a
temperature ranging as high as at least 250.degree. C. and a
pressure of up to at least 150 bar.
[0055] The exchanger 1' is installed in a vertical borehole 4' made
in a granite formation 5'. Under the effect of the pressure of the
supercritical CO.sub.2 fluid 3', the shell 2 is brought into direct
contact with the wall of the borehole 4'. The injection 6' and
return 7' of the heat-transfer fluid 3' are performed at the
surface end 8' of the upper part of the shell 2'.
[0056] The upper part of the exchanger 1' is contained in a
containment harness 9' made of Kevlar straps. It may be
manufactured from other aramid straps. The containment harness
constitutes a containment device the shape of which could differ
from that of a harness. The straps used have a width of 1 cm and
their cumulative width is 40 cm. The straps could have a different
width. The containment harness constitutes a containment device the
shape of which could differ from that of a harness.
[0057] The containment harness 9' extends over the upper part of
the shell, including its surface end 8'. It extends over a length
L1' of 1 m and is wedged between the bladder 2 and the granite
formation 5.
[0058] The exchanger 1' also comprises an inner tube 10' made of
silicone elastomer. This inner tube 10' has an opening 11' allowing
fluid to pass between the inside of the tube 10' and the outside of
the tube 10'.
[0059] The circulation of heat-transfer fluid 3' in the shell 2' is
thus organized from the inside of the tube 10' toward the outside
of the tube 10', as indicated by the three arrows in the shell 2'.
The direction of circulation in the shell 2' may be organized in
the opposite direction.
[0060] The silicone elastomer of which the inner tube 10' is made
has a low thermal conductivity so as to limit internal thermal heat
losses. The value of its thermal conductivity is of the order of
0.2 W/(m.K).
[0061] The shell 2' extends over a length L2' of 30 m. This length
may be different. It may vary from 12 to 30 m. Its diameter is 20
cm. It may be different and vary from 20 to 30 cm. The inside
diameter of the inner tube 10' is 120 mm. The diameter of the inner
tube may vary according to the diameter d' of the geothermal
exchanger 1'. It may be 200 mm when the diameter d' of the
geothermal exchanger is 30 cm. The thickness of its wall is 10 mm.
It may differ and vary from 10 to 30 mm.
[0062] For an internal pressure of 120 bar in the shell 2', the
load on the upper part of the exchanger 20 cm in diameter in
contact with atmospheric pressure is 38 000 daN. The Kevlar straps
used have a tensile strength of 1000 daN per cm of width. A
cumulative width of around 40 cm of straps distributed over the 62
cm of circumference of the bladder 2 makes it possible to
compensate for the load on the upper part of the exchanger. As it
is being pressurized, when the bladder 2' is not yet pressed firmly
against the wall of the hole, the resistance of the bladder 2' to
stretching is enough to hold the bladder 2' and the heat-transfer
fluid 3' in the borehole 4'. When the bladder 2' is pressed against
the wall of the borehole 4' by 120 bar of internal pressure, the
bladder 2' is held in place by the resistance of the walls of the
borehole and by the resistance of the containment harness 9'. As
the length of strap wedged between the bladder 2' and the granite
formation 5' is 1 m, the surface area of strap subjected to the
pressure of 120 bar is 100 cm.sup.2, which corresponds to a
crushing force on the strap of 12 000 daN, which means that a
tension of 1000 daN on the strap can be withstood.
[0063] The invention is not restricted to the embodiments set out
and other embodiments will be clearly apparent to those skilled in
the art.
* * * * *